Benzenediazonium tetrafluoroborate

Benzenediazonium tetrafluoroborate is an organic compound with the formula [C₆H₅N₂]BF₄. It is a salt of a diazonium cation and tetrafluoroborate. It exists as a colourless solid that is soluble in polar solvents. It is the parent member of the aryldiazonium compounds,^[1] which are widely used in organic chemistry.

Benzenediazonium tetrafluoroborate

Names
IUPAC name Benzenediazonium tetrafluoroborate
Other names Phenyldiazonium tetrafluoroborate
Identifiers
CAS Number	369-57-3
3D model (JSmol)	Interactive image
ChemSpider	4447548 N
EC Number	820-352-6
PubChem CID	5284485
CompTox Dashboard (EPA)	DTXSID5021467
InChI InChI=1S/C6H5N2.BF4/c7-8-6-4-2-1-3-5-6;2-1(3,4)5/h1-5H;/q+1;-1 Key: JNCLVGMBRSKDED-UHFFFAOYSA-N
SMILES [B-](F)(F)(F)F.C1=CC=C(C=C1)[N+]#N
Properties
Chemical formula	C6H5BF4N2
Molar mass	191.92 g·mol−1
Appearance	colorless crystals
Density	1.565 g/cm3
Melting point	decomposes
Boiling point	decomposes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N (what is YN ?) Infobox references

Synthesis

Diazotization of aniline with nitrous acid in the presence of hydrochloric acid gives phenyldiazonium chloride:

C₆H₅NH₂ + HNO₂ + HCl → [C₆H₅N₂]Cl + 2 H₂O

The required nitrous acid can be generated in situ by combining sodium nitrite and hydrochloric acid.^[2] The tetrafluoroborate salt of phenyl diazonium can be obtained from benzenediazonium chloride by salt metathesis using tetrafluoroboric acid.

[C₆H₅N₂]Cl + HBF₄ → [C₆H₅N₂]BF₄ + HCl

The tetrafluoroborate is more stable than the chloride.^[3]

Properties

Main article: Diazonium compound

The diazo group (N₂) can be replaced by many other groups, usually anions, giving a variety of substituted phenyl derivatives:

C₆H₅N₂⁺ + Nu⁻ → C₆H₅Nu + N₂

These transformations are associated with many named reactions including the Schiemann reaction, Sandmeyer reaction, and Gomberg–Bachmann reaction. A wide range of groups that can be used to replace N₂ including halide, SH⁻, CO₂H⁻, OH⁻. Of considerable practical value in the dye industry are the diazo coupling reactions.

Reaction with aniline gives 1,3-diphenyltriazene.^[4]

The structure of the salt has been verified by X-ray crystallography. The N-N bond distance is 1.083(3) Å.^[5]

Safety

Whereas the chloride salt is explosive,^[6] the tetrafluoroborate is readily isolated.